$45k tops. Why would it cost anymore if you left an SS as is? LS7s are not THAT expensive. You must subtract an LS3 from the price of that LS7. You can't add it on top of the price of an SS because you're not getting 2 engines. The harness needed and dry sump configured into the car? A 2SS would be $45k. 1SS $42k?

As good as this sounds,you can't just slap an LS7 in an SS and call it a day. Well,you could,but GM certainly isn't going to do it without the upgraded associated parts necessary to warranty it for 100k miles.